1. Field of the Invention
The present invention relates to power tools, particularly to hand-held vacuum-compression type percussion tools used in the construction industry for demolition of old buildings, pavement breaking, etc.
2. Description of Prior Art
The major problem experienced by the manufacturers of hand-held impact and percussion power tools is to find a compromise among three contradictory requirements, i.e., to provide high energy of impact, light weight of the power tool, and reduced level of vibrations on the power tool's housing. These requirements are dictated by strict sanitary norms.
However, the three requirements mentioned are interrelated so that satisfaction of one of them results in impairment of the others. For example, an increase in the impact energy leads to an increase in weight and level of vibrations. Attempts have been made previously to solve these problems by developing new improved hand-held percussion power tools.
One vacuum compression type power tool aimed at the solution of the above problem is described in my copending U.S. patent application No. 07/187,554 filed Apr. 28, 1988. This vacuum-compression type percussion power tool comprises a housing, a cylinder fixed in the housing, a piston reciprocating in the cylinder from a reciprocating drive mechanism such as a crank mechanism driven, e.g., by an electric motor, a working tool installed in the front part of the power tool, and a floating striker which slides inside the cylinder in a space between a tail portion of the working tool and the lower end of the piston. In addition to a main working chamber, the power tool is provided with a sealed auxiliary chamber which is connected with the main chamber through compensation holes and idle-stroke holes.
A check valve is installed in the wall of the auxiliary chamber. This check valve, which connects the auxiliary chamber with an atmospheric-pressure space between the housing and the cylinder, allows flow of air in a direction only from the above-mentioned atmospheric-pressure space to the auxiliary chamber. As a result, during several cycles after starting the power tool, an additional quantity of air will be sucked into the auxiliary chamber via the valve, so that after reaching established conditions, the auxiliary chamber and the main chamber will operate with an increased amount of air, and therefore, with an increased pressure at the commencement of each cycle. This will increase the energy of impact.
Although the power tool described in my above-mentioned patent application provides an increased energy of impact and has a reduced level of vibrations transmitted to the housing, this construction is effective only for power tools with the impact energy below 80 Joules. In the case where more powerful tool is required, e.g., for breaking extremely hard rocks and concretes, the above-described power tools appears to be insufficiently powerful.